std::chrono::operator+, std::chrono::operator- (std::chrono::year_month_weekday_last)

From cppreference.com
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
 
 
constexpr std::chrono::year_month_weekday_last

operator+(const std::chrono::year_month_weekday_last& ymwdl,

          const std::chrono::months& dm) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

operator+(const std::chrono::months& dm,

          const std::chrono::year_month_weekday_last& ymwdl) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

operator+(const std::chrono::year_month_weekday_last& ymwdl,

          const std::chrono::years& dy) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

operator+(const std::chrono::years& dy,

          const std::chrono::year_month_weekday_last& ymwdl) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

operator-(const std::chrono::year_month_weekday_last& ymwdl,

          const std::chrono::months& dm) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

operator-(const std::chrono::year_month_weekday_last& ymwdl,

          const std::chrono::years& dy) noexcept;
(since C++20)
1-2) Adds dm.count() months to the date represented by ymwdl. The result has the same year() and month() as std::chrono::year_month(ymwdl.year(), ymwdl.month()) + dm and the same weekday() as ymwdl.
3-4) Adds dy.count() years to the date represented by ymwdl. The result is equivalent to std::chrono::year_month_weekday_last(ymwdl.year() + dy, ymwdl.month(), ymwd.weekday_last()).
5) Subtracts dm.count() months from the date represented by ymwdl. Equivalent to ymwdl+ -dm.
6) Subtracts dy.count() years from the date represented by ymwdl. Equivalent to ymwdl + -dy.

For durations that are convertible to both std::chrono::years and std::chrono::months, the years overloads (3,4,6) are preferred if the call would otherwise be ambiguous.

Example

#include <iostream>
#include <chrono>
using namespace std::chrono;
 
int main()
{
    std::cout << std::boolalpha;
 
    constexpr auto ymwdl1 {Tuesday[last]/11/2021};
    auto ymwdl2 = ymwdl1;
    ymwdl2 = months(12) + ymwdl2;
    ymwdl2 = ymwdl2 - years(1);
    std::cout << (ymwdl1 == ymwdl2) << '\n';
}

Output:

true